Positional deviation detecting method and device manufacturing method using the same

ABSTRACT

A method of detecting a relative positional deviation between first and second objects by use of a first alignment mark provided on the first object and a second alignment mark provided on the second object, wherein the first alignment mark includes a first grating lens and a second grating lens having a mirror image of the first grating lens, and the alignment mark includes a third grating lens and a fourth grating lens having a mirror image of the third grating lens. The incidence position information of first light coming via the first grating lens and the third grating lens and incident upon a first predetermined plane, and the incidence position of second light coming via the second grating lens and the fourth grating lens and incident upon a second predetermined plane, are detected, on the basis of which the relative positional deviation between the first and second objects in a predetermined direction is detected.

This application is a divisional of application No. 09/192,193, filedNov. 16, 1998, now U.S. Pat. No. 6,285,033.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to a positional deviation detecting method, andto an exposure apparatus or a device manufacturing method using thesame. The present invention is particularly suitable for use in anexposure apparatus or a scan type exposure apparatus to be used in alithographic process for the manufacture of microdevices such assemiconductor devices (e.g., IC or LSI), image pickup devices (e.g.,CCD), display devices (e.g., liquid crystal panel) or magnetic heads,for example, for relative positioning or alignment between a firstobject such as a mask or reticle (hereinafter “mask”) and a secondobject such as a wafer when a fine pattern such as an electronic circuitpattern formed on the first object is to be lithographically transferredto the second object.

In exposure apparatuses for device manufacture, relative alignment of amask and a wafer is an important factor in improvement of performance.For a DRAM which is a representative semiconductor integrated circuit,an overall registration precision of about ⅓ to ¼ of the minimumlinewidth of a resolution pattern image is required. Particularly, inrecent exposure apparatuses, an alignment precision of 20 nm or less isrequired to meet further enlargement of integration of semiconductorchips.

For a 1-Gbit DRAM currently being developed, an overall registrationprecision of 40 nm to 50 nm is required and, within it, the precision tobe shared for the alignment precision will be 10-15 nm.

In many exposure apparatuses, a mask and a wafer are formed withpositioning marks, called alignment marks. A positional deviationbetween these alignment marks is optically detected and, on the basis ofa detected value, the positioning (alignment) of the mask and the waferis performed. As for detection of alignment marks, there are a method inwhich a mark is optically enlarged and projected on a CCD by which imageprocessing is performed; a method in which a straight diffractiongrating is used as a mark and the phase of diffractive light producedthereby is measured; and a method in which a zone plate (grating lens)is used as a mark and light diffracted by the zone plate is detectedupon a predetermined plane, whereby positional deviation of thediffracted light is detected.

Among these detection methods, the methods that use a straightdiffraction grating or a zone plate as an alignment mark have a featurethat, in the sense that detection is less influenced by any defect orfault of the mark, it is tough on the semiconductor process and enablesrelatively high precision alignment.

FIG. 1A is a schematic view of a position detecting system of aconventional type. In the drawing, parallel light emitted from a lightsource 72 passes through a half mirror 74 and, then, it is collected bya condenser lens 76 toward a convergence point 78. After this, the lightilluminates a mask alignment pattern 68 a upon the surface of a mask 68and a wafer alignment pattern 60 a upon the surface of a wafer 60. Thealignment patterns 68 a and 60 a each comprises a reflection type zoneplate which serves to define a spot of light convergence upon a planewhich is orthogonal to the optical axis, passing through the convergencepoint 78. A deviation of light convergence spot position upon that planeis detected by a detector 82, with the light being guided thereto by thecondenser lens 76 and another lens 80.

Control circuit 84 actuates a driving circuit 64 on the basis of anoutput signal from the detector 82, by which relative positioning of themask 68 and the wafer 60 is performed. FIG. 1B is a schematic view forexplaining the imaging relation of lights from the mask alignmentpattern 68 a and the wafer alignment pattern 60 a, shown in FIG. 1A.

In FIG. 1B, a portion of the light divergently emitted from the lightconvergence point 78 is diffracted by the mask alignment pattern 68 a,by which a light convergence point 78 a, representing the position ofthe mask, is defined adjacent to the point 78. Also, another portion ofthe light passes through the mask 68 as zeroth order transmissive lightand, with its wavefront unchanged, it impinges on the wafer alignmentpattern 60 a on the wafer 60 surface. After being diffracted by thepattern 60 a, the light passes through the mask 68 again as zeroth ordertransmissive light, and it is collected in the neighborhood of the lightconvergence point 78, whereby a light convergence point 78 brepresenting the position of the wafer is produced.

In FIG. 1B, when the light diffracted by the wafer 60 defines a lightconvergence spot, the mask 68 serves simply as a transparent member.

The position of the light convergence point 78 b thus produced by thewafer alignment pattern 60 a bears a deviation Δσ′ corresponding to adeviation Δσ of the wafer 60 with respect to the mask 68, in a direction(lateral direction) along the mask or wafer surface and along a planeperpendicular to the optical axis, passing through the light convergencepoint 78.

The amount of this deviation Δσ′ is measured with reference to anabsolute coordinate system defined upon a sensor, whereby the deviationΔσ is detected.

Usually, for alignment of a mask and a wafer based on detection of apositional deviation therebetween, the mask and the wafer are controlledto be placed with a mutual spacing in a predetermined range and,thereafter, they are brought into alignment on the basis of positionalinformation obtainable from a sensor by use of alignment patternsprovided on the mask and the wafer.

Such a method, however, involves a problem that Fraunhofer diffractionlight from openings of mask and wafer alignment marks enter a centralportion of a sensor, to cause interference with signal light thatresults in a decreased signal-to-noise ratio of a produced alignmentsignal as well as non-linearity of a signal to the mask-to-waferrelative deviation.

The influence of such Fraunhofer diffraction light may be reduced byarranging, as shown in FIG. 1C, a wafer alignment mark WA witheccentricity with respect to a mask alignment mark MA, in a state wherethere is no positional deviation between a mask circuit pattern and awafer circuit pattern. With this arrangement, since the Fraunhoferdiffraction light from the openings is spatially separated from thesignal light, the influence of interference is reduced and a good signalis produced.

With this method, however, since the wafer alignment mark WA has a shapeasymmetrical with respect to the alignment detecting direction, as shownin FIG. 1C, there is a problem that asymmetrical non-uniformness ofdiffraction efficiency is easily produced within the alignment mark.

If the diffraction efficiency distribution within the mark isasymmetric, a beam spot of signal light produced on a sensor becomesasymmetric. It causes a shift of the peak position and gravity centerposition of the spot, which leads to a detection error. The degree ofinfluence to asymmetry of a signal light spot of the asymmetry ofdiffraction efficiency distribution within the mark, becomes notablewith a larger deviation of the mask-to-wafer spacing (gap) with respectto a design gap, since it causes defocus of the spot.

The non-uniformness of diffraction efficiency within the mark may beattributable to the fact that: since an alignment mark has a power withrespect to the alignment direction, the pitch thereof (i.e., thelinewidth thereof) changes within the pattern, whereas it is difficultto control the linewidth and pattern step height (level difference) overthe whole wafer surface, with respect to every linewidth and throughoutthe etching process, the deposition process and so on of the deviceprocess.

Particularly, due to miniaturization of a circuit pattern, the linewidthof-a circuit pattern is 0.15 micron or less and the linewidth range ofan alignment mark is widened, from a few microns to about 10 microns.Further, the diameter of a wafer is enlarged. In consideration of thesetendencies, the problem of alignment detection error resulting fromnon-uniformness of linewidth or level difference of an alignment mark ofa wafer will become serious.

Further, in addition to the signal light diffracted by a mask alignmentmark and then by a wafer alignment mark and transmitted through a mask,there is unwanted diffractive light produced, which is transmittedthrough the mask alignment mark, diffracted by the wafer alignment mark,and then diffracted by the mask alignment mark. If the level differenceof the wafer alignment mark varies, the intensity ratio between thesignal light and such unwanted diffractive light changes, causing adetection error. Moreover, in relation to a global alignment processwhich is very advantageous with respect to throughput, there is aproblem that any local distortion due to a wafer process cannot becorrected.

While the problems described above all concern deterioration ofprecision which is attributable to a semiconductor process, there isanother problem of deterioration of registration precision which iscaused by a large sensitivity of an alignment detection system. Evenwhen an alignment mark is provided in good order, if the signal lighthas an angle θ to the optical axis (FIG. 1D), due to a set gap error δgof mask and wafer, the spot position displaces by tan(θ)·δg, causing adetection error.

Deterioration of registration precision attributable to the sensitivityof the alignment detecting system such as gap variation or deteriorationof registration precision resulting from deformation or local distortionof an alignment mark due to a process, as described above, is not aproblem solely peculiar to an alignment method using a zone plate orgrating lens but a problem also involved in the other alignment methodsdescribed hereinbefore.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a positionaldeviation detecting method in which appropriately set plural gratinglenses each having a power in a positional deviation detecting direction(X direction) are provided on a first object (mask) and a second object(wafer), and in which relative positional deviation between the mask andthe wafer can be detected very precisely on the basis of a deviation ofincidence position upon a predetermined plane of light coming from thegrating lenses of the mask and the wafer, such that high precisionalignment is assured.

It is another object of the present invention to provide an exposureapparatus and/or a device manufacturing method which uses such apositional deviation detecting method.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a positional deviation detecting systemof a conventional type.

FIG. 1B is a schematic and enlarged view of a portion of FIG. 1A.

FIG. 1C is a schematic view of an example of alignment marks of a knowntype.

FIG. 1D is a schematic view for explaining the function of aconventional positional deviation detecting system.

FIG. 2 is a schematic view of a main portion of a positional deviationdetecting system according to a first embodiment of the presentinvention.

FIG. 3A is a schematic view for explaining alignment marks usable in thefirst embodiment.

FIG. 3B is a schematic view for explaining a signal waveform on thesensor surface in the first embodiment.

FIG. 4 is a graph for explaining a signal characteristic in the firstembodiment of the present invention.

FIG. 5 is a schematic view for explaining the principle of positionaldeviation detection in the first embodiment of the present invention.

FIG. 6 is a schematic view of alignment marks usable in the firstembodiment of the present invention.

FIG. 7 is a schematic view for explaining the function of a positionaldeviation detecting system according to a second embodiment of thepresent invention.

FIG. 8 is a schematic view for explaining a signal waveform upon thesensor surface in the second embodiment of the present invention.

FIG. 9 is a schematic view of alignment marks usable in a positionaldeviation detecting system according to a third embodiment of thepresent invention.

FIG. 10 is a schematic view of a signal waveform upon the sensor surfacein the third embodiment of the present invention.

FIG. 11 is a schematic view of a main portion of a positional..deviationdetecting system according to a fourth embodiment of the presentinvention.

FIG. 12 is a schematic view of an alignment optical head according to anembodiment of the present invention.

FIG. 13 is a schematic view of alignment marks usable in the fourthembodiment of the present invention.

FIG. 14 is a schematic view of alignment marks usable in a positionaldeviation detecting system according to a fifth embodiment of thepresent invention.

FIG. 15 is a schematic view for explaining the relation between a maskand a wafer in a die-by-die alignment process in an embodiment of thepresent invention.

FIG. 16 is a schematic view for explaining the relation between a maskand a wafer in a-global alignment process in an embodiment of thepresent invention.

FIG. 17 is a flow chart for explaining the sequence of a combined globaland die-by-die alignment mode, in an embodiment of the presentinvention.

FIG. 18 is a schematic view for explaining selection of a die-by-dieshot, in an embodiment of the present invention.

FIG. 19 is a flow chart for explaining the sequence of wafer exposure,in an embodiment of the present invention.

FIG. 20 is a flow chart for explaining alignment mode selection, in anembodiment of the present invention.

FIG. 21 is a schematic view of alignment marks usable in a positionaldeviation detecting system according to a sixth embodiment of thepresent invention.

FIG. 22 is a schematic view of alignment marks usable in an embodimentof the present invention.

FIG. 23 is a flow chart of device manufacturing processes, in anembodiment of the present invention.

FIG. 24 is a flow chart for explaining a wafer process in the sequenceof FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A positional deviation detecting method and device manufacturing methodaccording to the present invention will now be described in detail withreference to preferred embodiments.

FIG. 2 is a schematic view of a main portion of a positional deviationdetecting system according to a first embodiment of the presentinvention. FIG. 3A is a schematic view for explaining diffraction oflight by alignment marks of FIG. 2. FIG. 3B is a schematic view forexplaining a signal waveform on the sensor surface in FIG. 2. FIG. 4 isa graph for explaining a signal characteristic under a relativepositional relation between a first object (mask) and a second object(wafer). FIG. 5 is a schematic view of light paths of an optical system,as expanded, in accordance with the positional deviation detectingmethod of FIG. 2. FIG. 6 is a schematic view of alignment marks of FIG.2.

In this embodiment, a positional deviation detecting system of thepresent invention is incorporated into an exposure apparatus for themanufacture of devices, using X-rays as an exposure light source. Inthese drawings, denoted at 1 is a mask (first object), and denoted at 2is a wafer (second object). Light from an alignment optical unit 19(19L, 19R) is projected onto an alignment mark 3 (3L, 3R) provided onthe mask 1, in an oblique direction, such that the alignment operationis performed without blocking the exposure light.

This structure provides the ability to hold the alignment optical unit19 fixed, such that alignment of the first and second objects 1 and 2 aswell as the exposure process can be performed in parallel. Particularly,this is very effective for improvement of throughput in an exposureapparatus using a die-by-die alignment method.

Components of this embodiment will be described in greater detail. InFIG. 2, on the mask 1, there are alignment marks (first alignment marksor mask side marks) 3L and 3R each comprising a Fresnel zone plate(grating lens) having a power only in the X direction, i.e., thedirection with respect to which positional deviation between the mask 1and the wafer 2 is to be detected. On the wafer 2, there are alignmentmarks (second alignment marks or wafer side marks) 4L and 4R eachcomprising a Fresnel zone plate (grating lens) having a power only inthe X direction and each to be positioned with respect to the maskalignment mark 3L or 3R.

Denoted at 19L and 19R are first and second alignment optical units eachfor detecting a positional deviation between the alignment marks 3L and4L (3R and 4R). These alignment optical units are mounted on movablestages 7L and 7R which are movable in X and Y directions. Since thealignment optical units 19L and 19R have the same structure, thefollowing description will be made of only one alignment optical unit19L.

Denoted at 10L is a semiconductor laser (light source). The lightemitted from the light source 10L goes through a light projecting lens11L and a half mirror 13L, and it is collected by a lens 14L. Then, thelight is reflected by a mirror 15L, and it is projected on the alignmentmark (first alignment mark) 3L on the mask 1 with a projection angle θ.The alignment mark 3L functions to project light in a direction (-Zdirection) of a normal of the mask 1, toward and upon the alignment mark(second alignment mark) 4L. The light thus projected on the mark 4L isdiffracted at an angle θ the same as the projection angle θ. Light 110which is provided by diffractive light from the mark 4L and which issimply passed through the mask 1, is reflected by the mirror 15L andthen passes through the lens 14L and half mirror 13L. Finally, it iscollected upon a sensor 12L. The sensor 12L comprises a one-dimensionalline sensor.

Denoted at 5 in FIG. 2 is a wafer chuck for holding the wafer 2 byattraction. Denoted at 6 is an X-Y-Z stage. The mask 1 and the wafer 2can be held with a predetermined spacing maintained therebetween, bymoving the Z stage.

While not shown in FIG. 2, in addition to the first and second alignmentoptical units 19L and 19R for detection of a deviation in the Xdirection, in this embodiment, there are alignment marks comprisingFresnel zone plates having a power in the Y direction which are providedon scribe lines upon the mask 1 and the wafer 2, for detection of apositional deviation in the Y direction. A third alignment optical unitfor detecting these alignment marks is provided.

Signals from sensors of these alignment optical units are applied to aCPU 16. The amount of deviation in the X direction is detected from anaverage of sensor outputs of the two alignment optical units forX-direction detection. The rotational amount is detected from thedifference between the outputs. The amount of deviation in the Ydirection is calculated from the sensor output of the Y-directionalignment optical unit. Positional deviations of a few shots on thewafer 2 are detected in this manner, and a signal is transmitted to astage moving driver 17 so as to bring the mask 1 and the wafer 2 intoalignment with each other in accordance with a global alignment methodor die-by-die alignment method, well known in the art. Both of thealignment optical units 19L and 19R are placed at positions not blockingthe exposure light (X-rays) within the exposure region.

Referring now to FIG. 12, the function of light projecting lens 11 (11L,11R) and light receiving lens 14 (14L, 14R) of the alignment opticalunit 19 (19L, 19R) of FIG. 2 will be described.

Light 20 from a light source 10 is once collected by the lightprojecting lens 11 and then it is reflected by a half mirror 13 towardthe lens 14. Here, the lenses 11 and 14 are so designed that, withrespect to the lens 14, the light convergence point 11 a defined by thelens 11 is placed substantially in an optically conjugate relation withthe mask 1. Thus, the projected beam spot on the mask 11 is slightlylarger than the alignment mark 3L or 3R. As regards the light receptionside, on the other hand, the convergence plane 23 of the light 110 isrelayed by the lens 14 to the sensor 12 at a unit magnification.

The basic principle of detection of positional deviation in thisembodiment of the present invention will be described with reference toFIG. 5. Although actually the light which is reflectively diffracted bya wafer 2 is used, FIG. 5 illustrates the structure in terms of atransmissive type lens equivalent to it. In FIG. 5, there is a light(1-1-0 light) diffracted at first order by the mask side mark 30 a (31a), then diffracted at first order by the wafer side mark 30 a (31 a)and then simply transmitted through the mask 1. Also, there is light(0-0-1 light) transmitted through the mask side mark 30 a (32 a), thendiffracted at first order by the wafer side mark 30 a (31 a) and thendiffracted by the mask side mark 30 a (31 a). The light paths of theselights are illustrated in superposition.

On the mask 1, there is an alignment mark (grating lens) 30 a comprisinga Fresnel zone plate having a power only in the X direction, which isformed on a scribe line. First order transmissively diffractive lightfrom the mark is being influenced by a light converging function.Another alignment mark (grating lens) 30 b is formed on a scribe line ofa wafer 2, and it comprises a Fresnel zone plate having a power only inthe X direction. By this mark, the reflectively diffractively light(shown as transmissive light in FIG. 5) is being influenced by a lightdiverging function. The diffraction light goes through the mask and iscollected upon the sensor 12.

The zone plate combination (grating lenses 30 a and 30 b) with which thelight is influenced by a convex lens function at the mask 1 side and isinfluenced by a concave lens function at the wafer 2 side, will bereferred to as a “convex-concave system”.

Additionally, the mask 1 and the wafer 2 are provided with an alignmentmark (grating lens) 31 a and an alignment mark (grating lens) 31 b eachcomprising a Fresnel zone plate having a power only in the X direction.These marks are formed on respective scribe lines on the mask and thewafer, and they are disposed adjacent to the alignment mark pair 30 aand 30 b of the convex-concave system. The alignment mark 31 a of themask 1 serves to apply a light diverging function to the first ordertransmissively diffractive light therethrough. The alignment mark 31 bof the wafer 2 serves to apply a light converging function to thereflectively diffractive light therefrom.

Here, the first alignment mark 3L of FIG. 2 corresponds to the alignmentmarks 30 a and 31 a, while the second alignment mark 4L corresponds tothe alignment marks 30 b and 31 b.

The combination of alignment marks (zone plates) 31 a and 31 b withwhich light is influenced by a concave lens function at the mask 1 sideand is influenced by a convex lens function at the wafer 2 side, will bereferred to as a “concave-convex system”. The light passing through theconcave-convex system is collected upon the sensor 12, like the lightpassing the convex-concave system.

What is described above concerns the light (1-1-0 light) diffracted atfirst order by the mask side mark (mask side alignment mark), thendiffracted at first order by the wafer side mark (wafer side alignmentmark) and then transmitted through the mask. Actually, as describedhereinbefore, the light (0-1-1 light) transmitted through the mask sidemark, then diffracted at first order by the wafer side mark and thendiffracted by the mask side mark is approximately collected at aposition adjacent to the 1-1-0 light.

FIG. 5 illustrates this. Denoted at 23 is the plane of light convergence(of the 1-1-0 light). If the focal lengths of the alignment marks 30 aand 31 a of the mask 1 are Fm₁ and Fm₂, the focal lengths of thealignment marks 30 b and 31 b of the wafer 2 are Fw₁ and Fw₂, thespacing between the mask 1 and the wafer 2 is g, and the distance fromthe mask 1 to the convergence plane 23 is L, then, with a deviation xbetween the mask 1 and the wafer 2 in the X direction, the positions S₁and S₂ of the light convergence points of the 1-1-0 light through theconvex-concave system (30 a, 30 b) and through the concave-convex system(31 a, 31 b), in the X direction along the light convergence plane, aregiven by the following equations:

S₁=[1−L/(Fm₁−g)]·x  (1)

S₂=[1−L/(Fm₂−g)]·x  (2)

On the other hand, the positions S₃ and S₄ of the light convergencepoints of the 0-1-1 light through the convex-concave system and throughthe concave-convex system, in the X direction along the lightconvergence plane 23, are given by the following equations:

S₃=[L′/(Fw₁−g)]·x  (3)

S₄=[L″/(Fw₂−g)]·x  (4)

where L′ and L″ are the distances of the convex-concave system and theconcave-convex system to the convergence position of 0-1-1 light and tothe mask 1, respectively.

For conditions necessary for assuring convergence of 1-1-0 light uponthe light convergence plane 23, the following relations are required:

1/(Fm₁−g)+1/L=−1/Fw₁  (5)

1/(Fm₂−g)+1/L=−1/Fw₂  (6)

In this embodiment, in order to provide a magnification of 100× for theposition S₁ with respect to the mask-to-wafer positional deviation x,numerical values may be L=18.7 mm, g=30 microns, Fm₁=214 microns, andFw₁=−184 microns.

On the other hand, as regards the magnification for the position S₂, inorder that a magnification −100× is provided with respect to themask-to-wafer positional deviation x, design values of focal lengths Fm₂and Fw₂ of the alignment marks 31 a and 31 b may be −240 microns and 270microns, respectively.

Here, from equations (1)-(4), as regards the amount of positionaldeviation (=S₁−S₃) upon the sensor 12 produced by the magnificationdifference between the 1-1-0 light (S₁) and 0-1-1 light (S₃) of theconvex-concave system, since it is smaller than the expansion of therespective beam spots, apparently they appear as a single spot B1 uponthe sensor 12 surface, as shown in FIG. 3B.

The same applies also to the 1-1-0 light (S₂) and 0-1-1 light (S₄) ofthe concave-convex system, and as a spot of the concave-convex system,apparently a single spot B2 is produced. Thus, by measuring the spotdistance d₁ between the light spots of the convex-concave system (30 a,30 b) and the concave-convex system (31 a, 31 b), the relativepositional deviation between the mask 1 and the wafer 2, being enlargedby about 200×, can be detected.

FIG. 6 illustrates the first and second alignment marks 3L and 4L on themask 1 and the wafer 2, respectively, used in this embodiment.

As shown in FIG. 6, there are mirror image marks (alignment marks) 30 amand 30 bm corresponding to inverted patterns of the alignment marks 30 aand 30 b, as well as mirror image marks (alignment marks) 31 am and 31bm of the alignment marks 31 a and 31 b, juxtaposed with each other.

Here, the alignment marks 30 a, 30 am, 31 a and 31 am, constituting thefirst alignment mark 3L, correspond, in order, to the first, second,fifth and sixth grating lenses. The alignment marks 30 b, 30 bm, 31 band 31 bm constituting the second alignment mark 4L correspond, inorder, to the third, fourth, seventh and eighth grating lenses.

Groups of alignment marks 30 am and 30 bm and alignment marks 31 am and31 bm will be referred to as “negative marks”. Upon the sensor 12, thereare produced four signal spots, i.e., positive mark convex-concavesystem spot B1, positive mark concave-convex system spot B3, negativemark convex-concave system spot B2 and negative mark concave-convexsystem spot B4. In a state wherein there is no deviation between themask 1 and the wafer 2, as shown in FIG. 3A, diffractive light from thepositive mark convex-concave system (30 a, 30 b) is being diffracted ina direction of −5 deg., while diffractive light from the positive markconcave-convex system (31 a, 31 b) is being diffracted in a direction of+2.5 deg. Diffractive light from the negative mark convex-concave system(30 am, 30 bm) which are mirror images of the positive marks, is beingdiffracted in a direction of +5 deg, while diffractive light from theconcave-convex system is being diffracted in a direction of −2.5 deg.Thus, as shown in FIG. 3B, the four signal spots B1-B4 are separatedfrom each other.

FIG. 4 illustrates the results of measurement of the spacing d₁ betweenthe positive mark convex-concave system spot B1 and the positive markconcave-convex system spot B3 as well as the spacing d₂ between thenegative mark convex-concave system spot B2 and the negative markconcave-convex system spot B4, measured at two gap levels as the waferis shifted relative to the mask. The magnification M of the spacing d₁to the mask-to-wafer deviation was M=210×, while the magnification m ofthe spacing d₂ to the mask-to-wafer deviation was m=−210×=−M.

It has been confirmed that, when the gap is changed, both of the spotspacings d₁ and d₂ change as offset in the direction enlarging (orreducing) the spot spacing, within the mask-to-wafer deviation range of±3 microns, as shown in FIG. 4 (the amount of spot change due to the gapchange is Eg, both for the spot spacings d₁ and d₂).

Next, changes of spot spacings d₁ and d₂ due to a change in wafer sidealignment mark caused by a semiconductor device manufacturing process,will be explained. As described hereinbefore, the four signal spotsB1-B4 are combined spots of two lights, i.e., 1-1-0 light and 0-1-1light. If, for example, regarding the positive mark spots B1 and B3, thebeam spot spacing between the 1-1-0 light and 0-1-1 light of theconcave-convex system is wider than the beam spot spacing between the1-1-0 light and 0-1-1 light of the convex-concave system, the spotspacing changes in the direction to be widened as the light quantity ofthe 0-1-1 light increases as compared with the light quantity of the1-1-0 light.

On the other hand, regarding the negative marks as defined by mirrorimages of the positive marks, the spot spacing changes in the directionto be widened as the light quantity of the 0-1-1 light increases ascompared with the light quantity of the 1-1-0 light. Here, the intensityratio between the 1-1-0 light and 0-1-1 light changes with a change inlevel difference of alignment mark, since the incidence angle upon thewafer alignment mark is different.

Also, since the alignment mark has a power with respect to thepositional deviation detecting direction, and since the grating pitch(linewidth) in the mark changes in the positional deviation detectingdirection, there occurs non-uniformness of resist film thickness on themark in accordance with the linewidth in the mark. This results innon-uniformness of diffraction efficiency within the-alignment mark.Such non-uniform diffraction efficiency produces deformation of beamspot shape, and causes a change in spot spacing.

If the spot spacing d₁ of the positive marks changes to be widened dueto non-uniformness of diffraction efficiency, the spot spacing d₂ of thenegative marks defined by mirror images of the positive marks, alsochanges in the same direction and by the same amount. Thenon-uniformness of a resist on a mark changes in dependence upon thecenter of the wafer, since usually the resist is applied thereto by aspin coating method. Further, the manner of change differs with thelevel difference of an underlying alignment mark or duty ratio, forexample.

The amount of change Ep of the spot spacing as the level difference ofunderlying mark or the non-uniformness of resist coating changes due toa process, is the same both for the spot spacings d₁ and d₂ and it is inthe same direction. Therefore, the spot spacings d₁ and d₂ can beexpressed, when the mask-to-wafer deviation is x, the magnification ofthe spot spacing to the mask-to-wafer deviation is M, the spot spacingin a state where there is no mask-to-wafer deviation is d₀, the amountof change in the spot spacing caused by a gap setting error is Eg, andthe amount of change in the spot spacing caused by a change of mark dueto a process is Ep, as follows:

d₁=M*x+Eg+Ep+d₀  (7)

d₂=−M*x+Eg+Ep+d₀  (8)

By calculating the sum of equations (7) and (8), the mask-to-waferdeviation x can be determined as follows:

x=(d₁−d₂)/2M  (9)

From equation (9), initial spot spacing d₀, spot spacing change Eg dueto gap setting error, and spot spacing change Ep due to a change inmark, all can be canceled. Therefore, by measuring the spot spacing d₁of the positive marks and the spot spacing d₂ of the negative marks, adeviation of the wafer with respect to the mask can be measured withoutbeing influenced by the gap setting error or a change of alignment mark.

Although this embodiment has been described with respect to an examplewherein the spacing di between the spots B1 and B3 and the spacing d₂between the spots B4 and B2 are detected and the mask-to-wafer deviationis calculated in accordance with equation (9), the mask-to-waferdeviation can be measured while canceling the spot spacing change Eg dueto gap setting error and the spot spacing change Ep due to a change of amark, by taking the spacing between the spots B1 and B4 as d₁ and takingthe spacing between the spots B2 and B3 as d₂.

Equation (9) can be considered in a different way. That is, it maycorrespond to that the spacing between an average position of theconvex-concave system beam position B1 and the convex-concave systemmirror image mark beam position B2 and an average position of theconcave-convex system beam position B3 and the concave-convex systemmirror image mark beam position B4, is measured. This may be measureddirectly, as a matter of course.

As regards the asymmetry of signal waveform resulting from deformationof the wafer side mark due to a process or from a gap setting error,since the mark is formed by a mirror image, the signal waveform will besuch as the mirror image signal waveform as illustrated in FIG. 3B.Therefore, the average position of the mirror image waveforms is lessinfluenced by the asymmetry of the waveform.

In this embodiment, in the manner described above, a positionaldeviation between a mask 1 and a wafer 2 is detected, and high precisionalignment of the mask and the wafer is accomplished.

FIG. 7 illustrates paths of alignment light according to a secondembodiment of the present invention, and FIG. 8 illustrates signalwaveforms in the second embodiment.

In the first embodiment, alignment signal light is received by one linesensor. In this embodiment, as compared therewith, diffractive lightsfrom convex-concave system marks and concave-convex system marks arereceived by separate line sensors 12 a and 12 b. This accomplishes analignment system of a wider detection range. The remaining portion hasessentially the same structure as that of the first embodiment.

Namely, disposition of alignment marks (positive and negative marks) aswell as powers in alignment direction (i.e., focal lengths of thelenses), for example, are designed essentially the same as those of thefirst embodiment.

In FIG. 7, the incidence angle θ₁ of alignment light of a wavelengthλ=830 nm is 12 deg., the diffraction angle θ₂ from a convex-concavesystem mark is 15 deg., and the diffraction angle θ₃ from aconcave-convex system mark is 20 deg. The Y-direction pitches of gratinglenses as the light is to be diffracted just downwardly (−Z direction)from the mask alignment mark, are set as follows.

Regarding the mask side alignment mark, the Y-direction pitch Pm of thegrating lenses is Pm=λ/sin (12 deg.)=3.99 microns. Regarding the waferside alignment mark, the Y-direction pitch Pw₁ of the convex-concavesystem grating lens is Pw₁=λ/sin (15 deg.)=3.21 microns, while theY-direction pitch Pw₂ of the concave-convex system grating lens isPw₂=λ/sin (20 deg.)=2.43 microns.

As shown in FIG. 8, the positions of the spots B1 and B2 upon the sensor12 a as well as the positions of the spots B3 and B4 upon the sensor 12b are detected, and the spacing d₁ between the spots B1 and B3 and thespacing d₂ between the spots B4 and B2 are determined. Then, inaccordance with equation (9) mentioned hereinbefore, the deviation xbetween the mask and the wafer is calculated.

FIG. 9 illustrates alignment marks used in a third embodiment of thepresent invention, and FIG. 10 illustrates signal waveforms in the thirdembodiment.

In the first embodiment, each of the first alignment mark 3L of the maskand the second alignment mark 4L of the wafer is provided by fourgrating lenses, and the mask-to-wafer deviation x is detected on thebasis of-four beam spots.

In this embodiment, as compared therewith, the first alignment mark 3Lof the mask comprises a convex lens 30 a, a convex lens 30 am (mirrorimage of the pattern 30 a), and a straight grating 35.

Also, the second alignment mark 4L of the wafer is provided by a concavelens 30 b, and a concave lens 30 bm (mirror image of the pattern 30 b).The sensor receives, as shown in FIG. 10, a light spot B1 having beendiffracted by the marks 30 a and 30 b and a light spot B2 having beendiffracted by the marks 30 am and 30 bm which are mirror image marks ofthe marks 30 a and 30 b.

Additionally, at the center thereof, the sensor receives a light spot B5of light diffracted by the straight grating 35 of the mask, then simplyreflected by the wafer and then transmitted through the mask.

The spacing d₁ between the light spots B1 and B5 and the spacing d₂between the light spots B5 and B2 are detected, and a mask-to-waferdeviation x is calculated in accordance with equation (9). The lightdiffracted by the straight grating 35 and diffraction grating 30 a hasno sensitivity to the mask-to-wafer deviation x. However, since thethree light spots displace in the same direction in response to any tiltof the wafer, by using this signal light, it is possible to remove theinfluence of the wafer tilt.

In this embodiment, the detection sensitivity becomes about a half ascompared with the first embodiment. However, there is an advantage thatthe area on the mask and the wafer to be occupied by the alignment marksdecreases significantly.

FIG. 11 is a schematic view of a main portion of a fourth embodiment ofthe present invention. In this embodiment, a positional deviationdetecting system of the present invention is incorporated into anexposure apparatus for the manufacture of devices, using X-rays as anexposure light source. In the drawing, denoted at 1 is a mask (firstobject), and denoted at 2 is a wafer (second object). The positioning(alignment) of the mask and the wafer is performed by using light froman alignment optical unit 19.

In FIG. 11, on the mask 1, there are alignment marks (first alignmentmarks) 3L and 3R each comprising a straight Fresnel zone plate (gratinglens) having a power only in the X direction, i.e., the direction withrespect to which positional deviation between the mask 1 and the wafer 2is to be detected. On the wafer 2, there are alignment marks (secondalignment marks) 4L and 4R each comprising a straight Fresnel zone plate(grating lens) having a power only in the X direction and each to bepositioned with respect to the mask alignment mark 3L or 3R.

Denoted at 19L and 19R are alignment optical units each for detecting apositional deviation between the alignment marks 3L and 4L (3R and 4R).These alignment optical units are mounted on movable stages 7L and 7Rwhich are movable in X and Y directions. Since the alignment opticalunits 19L and 19R have the same structure, the following descriptionwill be made only of one alignment optical unit 19L.

Denoted at 10L is a semiconductor laser (light source). The lightemitted from the light source 10L goes through a light projecting lens11L and a half mirror 13L, and it is collected by a lens 14L. Then, thelight is reflected by a mirror 15L, and it is projected on the alignmentmark (first alignment mark) 3L on the mask 1 perpendicularly. Thealignment mark 3L functions to project light in a direction (−Zdirection) of a normal of the mask 1, toward and upon the alignment mark(second alignment mark) 4L. The light thus projected on the mark 4L isdiffracted perpendicularly in the +Z direction. The diffractive light istransmitted through the mask 1, and it is reflected by the mirror 15L.Then, the light goes through the lens 14L and the half mirror 13L, andit is collected upon a sensor 12L. The sensor 12L comprises aone-dimensional line sensor.

Denoted at 5 in FIG. 11 is a wafer chuck for holding the wafer 2 byattraction. Denoted at 6 is an X-Y-Z stage. The mask 1 and the wafer 2can be held with a predetermined spacing maintained therebetween, bymoving the Z stage.

While not shown in FIG. 11, in addition to the first and secondalignment optical units 19L and 19R for detection of a deviation in theX direction, in this embodiment, there are alignment marks comprisingstraight Fresnel zone plates having a power in the Y direction which areprovided on scribe lines upon the mask 1 and the wafer 2, for detectionof a positional deviation in the Y direction. A third alignment opticalunit for detecting these alignment marks is provided.

Signals from sensors of these alignment optical units are applied to aCPU 16. The amount of deviation in the X direction is detected from anaverage of sensor outputs of the two alignment optical units forX-direction detection. The rotational amount is detected from thedifference between the outputs. The amount of deviation in the Ydirection is calculated from the sensor output of the Y-directionalignment optical unit. Positional deviations of a few shots on thewafer 2 are detected in this manner, and a signal is transmitted to astage moving driver so as to bring the mask 1 and the wafer 2 intoalignment with each other in accordance with a global alignment methodor die-by-die alignment method, well known in the art.

In this embodiment, in an exposure operation, the first, second andthird alignment optical units move away from the center of the shot, sothat they do not block the exposure light.

FIG. 13 is a conceptional view of first and second alignment marks 3Land 4L used in this embodiment. The focal lengths of theses marks aswell as the disposition of them are designed similarly as those of thefirst embodiment.

In FIG. 13, the first alignment mark 3L of the mask 1 comprises a convexlens mark 40 a, a concave lens 41 a, and mirror image marks 40 am and 41am of them. The second alignment mark 4L of the wafer 2 comprises aconcave lens 40 b, a convex lens 41 b, and mirror image marks 40 bm and41 bm of them. These marks are juxtaposed with each other.

Like the first embodiment, the spot spacings d, and d₂ of the beam spotsof diffraction lights from these grating lenses are detected, and amask-to-wafer positional deviation x is calculated on the basis of it.

As shown in FIG. 13, since this embodiment uses straight grating lenses,there is an advantage that making the alignment mark is easy.

While the foregoing embodiments have been described with reference toexamples of proximity type X-ray exposure apparatus, the presentinvention is similarly applicable to an X-ray reduction exposureapparatus or a reduction projection exposure apparatus that uses lightas exposure light.

Next, a fifth embodiment of the present invention will be described.This embodiment corresponds to a modified form of the precedingembodiment, and it is applied to an exposure apparatus for devicemanufacture. The whole structure of the apparatus may be similar to thatof the FIG. 2 embodiment, and in this embodiment the grating lenses inthe alignment marks 3L (4L) and 3R (4R) are replaced by grating lensesshown in FIG. 14.

In FIG. 14, on the mask 1 there are a zone plate 50 a having a convexlens function, and a zone plate 51 a having a concave lens function.These marks are disposed with their central axes placed witheccentricity in the alignment detecting direction. Also, on the mask 1there are mirror image marks 50 am and 51 am which correspond to mirrorimages of the zone plates 50 a and 51 a with respect to the Y axis, andwhich are formed at the mirror image positions, respectively.

On the other hand, on the wafer 2 there are a zone plate 50 b having aconcave lens function and a zone plate 51 b having a convex lensfunction, as well as mirror image marks 50 bm and 51 bm of them formedat the mirror image positions with respect to the Y axis. The focallengths of these grating lenses (zone plates) are similar to those ofthe first embodiment.

This embodiment differs from the first embodiment in that, while in thefirst embodiment, light is diffracted perpendicularly from the mask andthe beam spot is separated from the center of the sensor due to theeccentricity of the wafer side lens, in this embodiment, the mask sidemark is placed with eccentricity and diffraction light therefrom istilted toward the alignment detecting direction, by which the light isseparated-away from the central portion of the sensor such that it isnot influenced by noise at the sensor central portion.

As shown in FIG. 14, all the grating lenses 50 b, 51 b, 50 bm, and 51 bmof the wafer are placed with their central axes registered with thecentral axes of the respective marks (i.e., symmetrical mark shapestructure).

Therefore, the beam profile of the diffraction light therefrom has asymmetric shape. Namely, even if the diffraction efficiency varies independence upon the pitch in the grating due to a process, the beam spotdeforms while maintaining the symmetry of the beam profile. As a result,a change in gravity center position of each beam spot becomes verysmall. The dependency upon the process is therefore small.

Like the first embodiment, if the distance between the beam spot gravitycenter position B1 of the convex-concave system (50 a, 50 b) and thebeam spot gravity center position B3 of the concave-convex system (51 a,51 b) upon the sensor is d₁, and the distance between the beam spotgravity center position B2 of light from the convex-concave systemmirror image marks 50 am and 50 bm and the beam spot gravity centerposition B4 of the concave-convex system mirror image marks 51 am and 51bm upon the sensor is d₂, then in equations (7) and (8) it can beapproximated that Ep=0.

By taking the sum of equations (7) and (8), the following relationapplies:

Eg=(d₁+d₂)/2+₀  (10)

The spacing (gap) g between the mask 1 and the wafer 2 can be expressed,while taking the magnification as m and the offset as g₀, as follows:

g=(d₁+d₂)/m+g₀  (11)

It has been confirmed that, in a case where, as in equation (11), thedeviation in the lateral direction (X direction) is small (not greaterthan 3 microns), without being dependent upon the positional deviation,the detection with respect to the gap direction (Z direction) isaccomplished at a precision of a submicron order. As regards the offsetg₀, calibration of it by use of any other gap sensor (e.g.,electrostatic capacitance sensor) is necessary.

Next, the positioning method according to this embodiment will bedescribed. FIG. 15 illustrates the relation between a mask 1 and a wafer2 in a case where a die-by-die alignment method in which the positioningis performed with respect to every shot, is used. At (A) in FIG. 15, apredetermined shot of the wafer 2 is brought to a position below themask 1 with the stage precision and, thereafter, positional deviationmeasurement as well as gap measurement are performed. If the gap setposition is beyond a predetermined amount, gap adjustment is made and,subsequently, positional deviation (shift and rotation) is adjusted intoa predetermined tolerance.

Subsequently, at (B) in FIG. 15, the exposure operation is performedand, thereafter, the wafer stage 15 is moved stepwise toward the nextshot position, as shown at (C) in FIG. 15. As above, the case whereinthe alignment measurement gap (Ga), the gap measurement gap (Gg), theexposure gap (Ge) and the step gap (Gs) are all the same, isadvantageous with respect to the throughput.

Of course, in a proximity exposure apparatus, the smaller the exposuregap is, the better the resolution is. Therefore, the alignment gap (Ga)and the gap measurement gap (Gg) as well as the step gap (Gs) may be thesame (for example, Ga=Gg=Gs=30 microns), and only the exposure gap (Ge)may be set small (e.g., Ge=15 microns).

At (B) in FIG. 15, on the basis of the gap as measured at the alignmentgap, the Z-axis stage is moved so that the exposure gap is brought to apredetermined level and, thereafter, the exposure a operation is done.

In this embodiment, the mask and the wafer are provided with marks andthe gap measurement is made by using diffraction light from these marks.Therefore, for exposure of a first layer, a separate gap measurementmark should be provided on the mask by which the gap measurement can beperformed without any mark on the wafer. An example is disclosed inJapanese Laid-Open Patent Application No. 2-167413.

Referring to FIG. 16, a sequential operation of global alignment inwhich the shot layout on a wafer is measured and the wafer stage axis isbrought into registration with it, will be explained.

At (A) and (B) in FIG. 16, positional deviations of and gaps at a fewpredetermined shots are measured, and a deviation between the layout ofshots transferred to the wafer and the wafer stage axis of the exposureapparatus is detected. Then, correction amounts for every shot isdetermined. Further, from the gap measured values, information about thewafer surface shape is detected.

At (C) in FIG. 16, the shot layout deviation is corrected, and the waferstage is stepped to the exposure shot. Further, on the basis of thewafer surface shape data, the gap setting is performed. At (D) in FIG.16, the exposure process a is performed.

Subsequently, the operations at (C) and (D) in FIG. 16 are repeated. Asregards gap set value, one of the following two may be selected:

Gm=Gms≠Ges=Ge

or

Gm=Gms=Ges=Ge.

In any of the die-by-die alignment method and the global alignmentmethod, the positional deviation measurement and the gap measurement canbe performed with the same gap (Gm=Ga=Gg) as in this embodiment. This isadvantageous with respect to the throughput, as compared with an examplewhere gaps are different.

If positional deviation measurement (and gap measurement) can be madeeven at the exposure position, as in this embodiment, there is anotherand significant advantage. In a global alignment procedure, as for shotlayout transformation parameters, generally six parameters of shift (Sx,Sy), rotation (Rx, Ry) and scale (Bx, By) are used to transform thepolar coordinate system with a linear formula. In such a case, however,there are two problems involved:

(a1) A local distortion component caused by a difference in waferprocess or wafer chucking state cannot be corrected; and

(a2) A positional deviation measurement error at an alignmentmeasurement shot applies influence to all the shots.

These two problems can be solved by the present invention. As regardsthe first problem (a1), in this embodiment as shown in FIG. 17, globalalignment is made in a usual way and, after stepwise motion to theexposure shot, a positional deviation is measured again. In a case wherethe wafer shot position is in the polar coordinate system having beenlinearly transformed, the positional deviation at this moment issubstantially zero.

However, for a shot where local distortion is produced, as shown in FIG.18, the positional deviation increases largely. Thus, a certaintolerance is set (in this embodiment, shift 20 nm and rotation 0.2urad), and there is a mode prepared by which, for a shot beyond thistolerance, the X and Y deviations and chip rotation are corrected, likethe die-by-die mode. This is a combined global and die-by-die mode.

Further, if the gap measured value is over the tolerance, it iscorrected by use of the Z tilt stage.

For the same process lot or if the combination of steppers used is thesame, the position where local distortion is produced has a goodreproducibility. Therefore, preferably, measurement data of thealignment detecting system at the exposure operation may be calibratedon the basis of data of a registration precision inspection system,obtainable by use of a preceding wafer or wafers, and after that theglobal alignment may be made mainly, with die-by-die alignment andexposure being specifically made to a shot having large localdistortion.

The second problem (a2) described above can be solved as follows. FIG.19 shows the procedure in which a few wafers are exposed as precedingwafers, prior to a start of the exposure for the lot.

As illustrated, when global alignment is executed, the exposureoperation is performed while positional deviations of shots are measuredas detection values of the alignment system. After the exposureoperation, a registration precision inspection system is used to detectthe precision of registration, in regard to every shot, between apattern already printed on the shot and the pattern just transferred toit, whereby a registration precision inspection value is obtained.

After that, the alignment mode to be selected for the succeeding wafersis determined. The alignment system of this embodiment of the presentinvention has three alignment modes, and the flow chart of FIG. 20illustrates the selection of alignment mode. In FIG. 20, at a firststep, on the basis of the registration precision inspection value,correction is made by use of the six parameters of shift (Sx, Sy),rotation (Rx, Ry) and scale (Bx, By). From the remainder, the positionof local distortion and its amount are determined.

At a second step, from a difference between the positional deviationmeasured value and the registration precision inspection value, themeasurement error amount of the alignment detecting system and thecorresponding shot are detected. If there is no measurement false shot(with a difference greater than a predetermined value) and thelimitation to the throughput is loose, the die-by-die alignment mode (A)is selected, and the exposure operation is performed.

If there is no measurement false shot but there is a strict limitationto the throughput the combined global and die-by-die alignment mode (B)is selected, and the exposure operation is performed. If there is ameasurement false shot in the alignment system, optimization of acombination of global alignment shots (i.e., those shots to be measuredbeforehand at the global alignment operation) is performed.

As regards this optimization, from those shots other than themeasurement false shot, detected values of an imaginary globalmeasurement shot number (e.g., four shots) is extracted. On the basis ofthis value, the six parameters of shift (Sx, Sy), rotation (Rx, Ry) andscale (Bx, By) with which the imaginary global measurement shot numberis minimized, are calculated, and by using these parameters, thedetected values of all the shots are corrected.

This calculation operation is made with respect to all the combinationsof global measurement shots. Among them, a combination of measurementshots with which dispersion of detected values after being corrected isminimized, is selected. With this procedure, any false reading of thealignment detecting system is not included in the global alignmentmeasurement shots, such that deterioration of registration precision dueto a false process can be prevented.

In a case where there is a false shot or a case where there is no falseshot but the local distortion is small and the throughput is strict, thesole global alignment mode (C) is selected.

Next, a sixth embodiment of the present invention will be described.This embodiment corresponds to a modified form of the precedingembodiment, and it is applied to an exposure apparatus for devicemanufacture. The whole structure of the apparatus may be similar to thatof the first embodiment of FIG. 2, and in this embodiment the gratinglenses in the alignment marks 3L (4L) and 3R (4R) are replaced bygrating lenses shown in FIG. 21.

In FIG. 21, on the mask 1 there are a zone plate 55 a having a convexlens function, and a zone plate 56 a having a concave lens function.These marks are disposed with their central axes placed witheccentricity in the alignment detecting direction. Also, on the mask 1there are mirror image marks 55 am and 56 am which correspond to mirrorimages of the zone plates 55 a and 56 a with respect to the Y axis, andwhich are formed at the mirror image positions, respectively.

On the other hand, on the wafer 2 there are a zone plate 55 b having aconcave lens function and a zone plate 56 b having a convex lensfunction, as well as mirror image marks 55 bm and 56 bm of them formedat the mirror image positions with respect to the Y axis.

The focal lengths of these grating lenses (zone plates) are similar tothose of the fifth embodiment.

This embodiment differs from the fifth embodiment in the shape (opening)of the mask side mark. In the fifth embodiment, the mark has arectangular shape. Diffraction light from it is influenced by Fraunhoferdiffraction, such that there are produced perpendicular side-lobes atsides of the mark, such as shown in FIG. 22 at (A). It is thereforenecessary that the measurement is made at the position where theside-lobes of the two beam spots do not influence upon each other.

With the alignment marks used in this embodiment, as compared therewith,side-lobes are produced in directions away from the sensor surface, suchas shown in FIG. 22 at (B). Therefore, the signal spots can be placedclose to each other. This allows to make small the numerical aperture(NA) of the light receiving lens in the alignment detecting system, suchthat the alignment detecting system can be made smaller in size.Alternatively, if the same alignment detecting system is used, themeasurement dynamic range can be advantageously widened.

While this embodiment uses a mask side mark of hexagonal shape, anyother shape (polygonal shape) may be used with similar advantageouseffects, provided that side-lobes are produced in a direction away fromthe sensor. Further, not only the mask side mark but also the wafer sidemark may be formed with a hexagonal shape.

Next, an embodiment of a semiconductor device manufacturing method whichuses a projection exposure apparatus such as described above, will beexplained.

FIG. 23 is a flow chart of a procedure for the manufacture ofmicrodevices such as semiconductor chips (e.g., ICs or LSIs), liquidcrystal panels, CCDs, thin film magnetic heads or micro-machines, forexample.

Step 1 is a design process for designing a circuit of a semiconductordevice. Step 2 is a process for making a mask on the basis of thecircuit pattern design. Step 3 is a process for preparing a wafer byusing a material such as silicon. Step 4 is a wafer process which iscalled a pre-process wherein, by using the so prepared mask and wafer,circuits are practically formed on the wafer through lithography. Step 5subsequent to this is an assembling step which is called a post-processwherein the wafer having been processed by step 4 is formed intosemiconductor chips. This step includes an assembling (dicing andbonding) process and a packaging (chip sealing) process. Step 6 is aninspection step wherein an operation check, a durability check and so onfor the semiconductor devices provided by step 5, are carried out. Withthese processes, semiconductor devices are completed and they areshipped (step 7).

FIG. 24 is a flow chart showing details of the wafer process. Step 11 isan oxidation process for oxidizing the surface of a wafer. Step 12 is aCVD process for forming an insulating film on the wafer surface. Step 13is an electrode forming process for forming electrodes upon the wafer byvapor deposition. Step 14 is an ion implanting process for implantingions to the wafer. Step 15 is a resist process for applying a resist(photosensitive material) to the wafer. Step 16 is an exposure processfor printing, by exposure, the circuit pattern of the mask on the waferthrough the exposure apparatus described above. Step 17 is a developingprocess for developing the exposed wafer. Step 18 is an etching processfor removing portions other than the developed resist image. Step 19 isa resist separation process for separating the resist material remainingon the wafer after being subjected to the etching process. By repeatingthese processes, circuit patterns are superposedly formed on the wafer.

With these processes, high density microdevices can be manufactured.

In accordance with the embodiments of the present invention as describedabove, a first object (mask) and a second object (wafer) are providedwith appropriately set plural grating lenses each having a power in thepositional deviation detecting direction (X direction), and a relativepositional deviation between the mask and the wafer can be detected athigh precision on the basis of a deviation of incidence positions, upona predetermined plane, of spots of light coming from the grating lensesof the mask and the wafer. Thus, a positional deviation detecting methodand/or a device manufacturing method based on it, by which highprecision alignment is accomplished, is provided.

Particularly, in a case where a mask and a wafer are provided withgrating lenses having a power in a positional deviation detectingdirection (X direction) and a positional deviation between the mask andthe wafer is detected on the basis of a positional deviation of lightspots through the grating lenses of the mask and the wafer, there may beprovided first and third grating lenses effective to enlarge the spotspacing of diffraction lights, for a mask-to-wafer positional deviation,as well as second and fourth grating lenses having patternscorresponding to mirror images of the first and third grating lenseswith respect to the mark center line (Y axis) and being effective toreduce the spot spacing, for the mask-to-wafer positional deviation, thesecond and fourth grating lenses being juxtaposed with the first andthird grating lenses. Positional deviation between the mask and thewafer and the spacing therebetween may be detected by using a first spotB1 obtainable from diffraction lights from the first and third gratinglenses and a second spot B2 obtainable from diffraction lights from thesecond and fourth grating lenses. This reduces the influence ofvariation in the semiconductor manufacturing process such asnon-uniformness of diffraction efficiency in the wafer side gratinglens, or the influence of gap setting error, such that higher precisiondetection of positional deviation is assured.

As a result, the yield of semiconductor chips can be enlarged.Additionally, the gap setting precision can be lowered. This iseffective to increase the throughput of a semiconductor exposureapparatus.

A mask and a wafer may be provided with alignment marks, and first andsecond alignment optical heads may be disposed at positions not blockingor absorbing the exposure light. Alignment light may be projectedobliquely, and light from alignment marks may be received. This enablespositional deviation detection and gap measurement, at the exposureposition.

For execution of global alignment, positional deviations may be detectedprior to exposure of shots. Registration errors of an exposed wafer orwafers may be measured, and on the basis of the positional deviationmeasured values and registration measured values, selection of a globalalignment mode, a combined global and die-by-die alignment mode and adie-by-die alignment mode may be made. This enables high precisionalignment and exposure, without being influenced by a false reading ofan alignment system due to a wafer process or any local distortion.

By comparing positional deviation measured values of shots by thealignment system with registration measured values, a false shot of thealignment system may be determined and it may be excluded out of theglobal measurement shots. Global measurement shots with whichregistration errors of shots on the whole wafer surface are minimized,may be selected. This enables high precision positioning and exposurewithout being influenced by false reading of an alignment system due toa wafer process.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. A method of detecting a relative positionaldeviation between a first object and a second object, opposed to eachother, with respect to a predetermined direction by use of a firstalignment mark provided on the first object and a second alignment markprovided on the second object, said method comprising: a first step forproviding the first alignment mark by use of a first grating lens, afifth grating lens, a second grating lens having a mirror image of thefirst grating lens, and a sixth grating lens having a mirror image ofthe fifth grating lens; a second step for providing the second alignmentmark by use of a third grating lens, a seventh grating lens, a fourthgrating lens having a mirror image of the third grating lens, and aneighth grating lens having a mirror image of the seventh grating lens; athird step for detecting an incidence position of first light coming viathe first grating lens and the third grating lens and incident upon afirst predetermined plane; a fourth step for detecting an incidenceposition of second light coming via the second grating lens and thefourth grating lens and incident upon a second predetermined plane; afifth step for detecting an incidence position of third light coming viathe fifth grating lens and the seventh grating lens and incident upon athird predetermined plane; a sixth step for detecting an incidenceposition of fourth light coming via the sixth grating lens and theeighth grating lens and incident upon a fourth predetermined plane; anda seventh step for detecting a relative positional deviation d_(x)between the first and second objects in the predetermined direction, onthe basis of a spacing d₁ between the first and third lights and aspacing d₂ between the second and fourth lights, and in accordance withan equation d_(x)=(d₁-d₂)/M, wherein M is the magnification of the spotspacing to the first-to-second object deviation.
 2. A method accordingto claim 1, wherein the incidence positions of the first and thirdlights are detected by use of a first sensor, and wherein the incidencepositions of the second and fourth lights are detected by use of asecond sensor.
 3. A method according to claim 1, wherein the first andseventh grating lenses serve as a convex lens, and wherein the third andfifth grating lenses serve as a concave lens.
 4. A method according toclaim 3, wherein the second and eighth grating lenses serve as a convexlens, and wherein the fourth and sixth grating lenses serve as a concavelens.
 5. A method according to claim 1, wherein the predetermineddirection is one of a direction parallel to the first and second objectsand a direction along which the first and second objects are opposed toeach other.
 6. A method of detecting a relative positional deviationbetween a first object and a second object, opposed to each other, withrespect to a predetermined direction by use of a first alignment markprovided on the first object and a second alignment mark provided on thesecond object, said method comprising: a first step for providing thefirst alignment mark by use of a first grating lens, a fifth gratinglens, a second grating lens having a mirror image of the first gratinglens, and a sixth grating lens having a mirror image of the fifthgrating lens; a second step for providing the second alignment mark byuse of a third grating lens, a seventh grating lens, a fourth gratinglens having a mirror image of the third grating lens, and an eighthgrating lens having a mirror image of the seventh grating lens; a thirdstep for detecting an incidence position of first light coming via thefirst grating lens and the third grating lens and incident upon a firstpredetermined plane; a fourth step for detecting an incidence positionof second light coming via the second grating lens and the fourthgrating lens and incident upon the first predetermined plane; a fifthstep for detecting an incidence position of third light coming via thefifth grating lens and the seventh grating lens and incident upon asecond predetermined plane; a sixth step for detecting an incidenceposition of fourth light coming via the sixth grating lens and theeighth grating lens and incident upon the second predetermined plane;and a seventh step for detecting a relative positional deviation betweenthe first and second objects in the predetermined direction, on thebasis of an average position of incidence positions of the first andfourth lights and an average position of incidence positions of thesecond and third lights.
 7. A method of detecting a relative positionaldeviation between a first object and a second object, opposed to eachother, with respect to a predetermined direction by use of a firstalignment mark provided on the first object and a second alignment markprovided on the second object, said method comprising: a first step forproviding the first alignment mark by use of a first grating lens, afifth grating lens, a second grating lens having a mirror image of thefirst grating lens, and a sixth grating lens having a mirror image ofthe fifth grating lens; a second step for providing the second alignmentmark by use of a third grating lens, a seventh grating lens, a fourthgrating lens having a mirror image of the third grating lens, and aneighth grating lens having a mirror image of the seventh grating lens; athird step for detecting an incidence position of first light coming viathe first grating lens and the third grating lens and incident upon afirst predetermined plane; a fourth step for detecting an incidenceposition of second light coming via the second grating lens and thefourth grating lens and incident upon a second predetermined plane; afifth step for detecting an incidence position of third light coming viathe fifth grating lens and the seventh grating lens and incident upon athird predetermined plane; a sixth step for detecting an incidenceposition of fourth light coming via the sixth grating lens and theeighth grating lens and incident upon a fourth predetermined plane; anda seventh step for detecting a relative positional deviation between thefirst and second objects in the predetermined direction, on the basis ofan average position of incidence positions of the first and secondlights and an average position of incidence positions of third andfourth lights.
 8. A method according to claim 6, wherein the first andsecond predetermined planes are defined on the same plane and whereinlight receiving means is provided on that plane.
 9. A method accordingto claim 7, wherein the first and second predetermined planes aredefined on the same plane and wherein light receiving means is providedon that plane.